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Nicholas of Cusa proposes (but apparently never performs) an experiment in which a plant is weighed and then planted in a container containing a weighed amount of soil. After a period of growth, the final weights of plant and soil, as well as the total weight of water applied, are determined and compared to the initial values. He speculates this will demonstrate that the mass of the plant was derived from water rather than soil.
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Jean Baptiste van Helmont performs the experiment proposed by Nicholas of Cusa nearly 200 years earlier. He concludes that the entire mass of the plant came from water, but ignores a very slight decrease in the weight of the soil.
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Edme Mariotte proposes that plants obtain part of their nourishment from the atmosphere.
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Stephen Hales writes that plant leaves "very probably" take in nourishment from the air, and that light may also be involved.
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Charles Bonnet observes the emission of gas bubbles by a submerged illuminated leaf.
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Joseph Priestley finds that air which has been made "noxious" by the breathing of animals or burning of a candle can be restored (i.e., made to support breathing or combustion again) by the presence of a green plant. He isolates the gas later identified as oxygen.
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Antoine Lavoisier begins to investigate and later names oxygen. He recognizes that it is consumed in both animal respiration and combustion. His work discredits the theory of "phlogiston," a hypothetical substance then believed to be emitted during respiration or combustion, and lays the foundations of modern chemistry.
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Jan Ingenhousz discovers that only the green parts of plants release oxygen and that this occurs only when they are illuminated by sunlight.
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Jean Senebier demonstrates that green plants take in carbon dioxide from the air and emit oxygen under the influence of sunlight.
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Pierre Joseph Pelletier and Joseph Bienaime Caventou give the name "chlorophyll" to the green pigment in plants.
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Rene Dutrochet makes the connection between chlorophyll and the ability of plants to assimilate carbon dioxide. Also identifies stomata on leaf surfaces.
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Matthias Schleiden postulates that the water molecule is split during photosynthesis.
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Hugo von Mohl makes detailed observations of the structure of chloroplasts.
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Julius Robert von Mayer proposes that the sun is the ultimate source of energy utilized by living organisms, and introduces the concept that photosynthesis is a conversion of light energy into chemical energy
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Jean Baptiste Boussingault makes accurate quantitative measurements of carbon dioxide uptake and oxygen production, a step leading to a balanced equation for photosynthesis: 6CO2 + 12H2O + light energy ----> C6H12O6 + 6O2 + 6H2O